Natural insulator contamination test results on various shed shapes in heavy industrial contamination area in Shanghai under AC energized and de-energized conditions

Insulator natural contamination tests on various shed shapes were conducted at two representative sites in Shanghai for one year. Equivalent salt deposit density (ESDD) was measured periodically, under the de-energized condition. Insulators energized at two sites for one year were removed and withstand voltage tests were conducted in artificial fog. Unexpectedly high ESDD values over 1 mg/cm² and NSDD (non-soluble deposit density) values over 5 mg/cm² were measured near a steel plant. Aerodynamic type insulators showed smaller ESDD values in general compared with deep-rib type insulators. SiO₂ (quartz) and CaSO₂-1/2H₂O (bassanite) were identified as the most dominant soluble contaminants